Conventionally, a sealing device shown in FIG. 15 is used between a hydraulic cylinder and a piston. FIG. 15 is a schematic half sectional view of the prior-art sealing device.
The sealing device 100 is for sealing an annular gap 400 between an inner peripheral face 201 of the cylinder 200 and an outer peripheral face 301 of the piston 300 and is fitted in an annular groove 302 formed in the outer peripheral face 301 of the piston 300. The sealing device 100 is formed of a resin seal ring 101 for sliding against the inner peripheral face 201 of the cylinder 200 and an elastic ring 102 fitted between the seal ring 101 and a groove bottom 303 of the annular groove 302 to give enlarging force to the seal ring 101.
In such a sealing device, an oil film made of lubricating oil is formed on a sliding surface between the seal ring 101 and the inner peripheral face 201 of the cylinder 200, which suppresses wearing and sliding resistance of the sliding surface and prevents occurrence of an unusual noise, stick slip, production of heat, and the like.
Provision of grooves in order to introduce the lubricating oil into the sliding surface of the seal ring to more reliably form the lubricating film or to maintain the lubricating film for a longer period of time is described in Patent Documents 1 and 2, for example.
Patent Document 1: Japanese Patent Application Laid-Open No. 2001-304413
Patent Document 2: Japanese Utility Model Application Laid-Open No. 07-043672